Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session L40: High Pressure |
Hide Abstracts |
Sponsoring Units: DCMP DMP Chair: Renata Wentzcovitch, University of Minnesota Room: Morial Convention Center 232 |
Tuesday, March 11, 2008 2:30PM - 2:42PM |
L40.00001: Complexity in `simple' metals Bruno Rousseau, Neil W. Ashcroft In electronic and structural terms, the light alkalis have long been regarded as `simple systems', at least under ordinary conditions. However, when compressed they exhibit unforeseen complexity; the melting curve of sodium, for example, has a striking maximum, falling to near room temperature melting where a complex structure (CI16) is found, this being in the cubic class but with 16 atoms per unit cell [1,2]. The light alkalis have been extensively studied using ab initio methods with standard assumptions of transferability made for the key pseudopotential input information, largely atomic based. Lacking still, however, is a somewhat more intuitive and physical understanding of the developments in electronic structure with progressive increase in density. In the present work, the problem is treated with non-linear response theory and non-overlapping pseudopotentials, and the structural complexity traced to effective ion-ion interactions with features that both at short range and long display competing state dependence. \newline [1] Gregoryanz et al., Phys. Rev. Lett. 94, 185502 (2005) \newline [2] McMahon et al., Chem. Soc. Rev. 35, 943 (2006) [Preview Abstract] |
Tuesday, March 11, 2008 2:42PM - 2:54PM |
L40.00002: High Pressure and Temperature Behavior of Lithium and Lithium Compounds Amy Lazicki, Alex Goncharov, Maddury Somayazulu, Viktor Struzhkin, Ho-kwang Mao, Russell Hemley Emerging structural complexity and unexpected increase of superconducting transition temperature at high pressure in lithium are some of the recently seen phenomena which indicate that our understanding of the behavior of this element at extreme conditions is incomplete. The heavier alkali metals (as well as alkaline earths and a variety of other elements) exhibit a maximum in the melting curve at high pressure, often attributed to the s-d electronic transition but recently shown most dramatically in light-weight sodium [1] at pressures below the expected s-d transition. In the interest of further exploring the origin of this high pressure-temperature behavior, we will present results of a study of lithium and lithium compounds in a resistively heated diamond anvil cell. [1] E. Gregoryanz, O. Degtyareva, M. Somayazulu, R. J. Hemley, and H. Mao, \textit{Phys. Rev. Lett}. \textbf{94}, 185502 (2005). [Preview Abstract] |
Tuesday, March 11, 2008 2:54PM - 3:06PM |
L40.00003: An improved multiphase equation of state for beryllium Gregory Robert, Arnaud Sollier, Philippe Legrand In our previous articles on beryllium (1)(2), a new theoretical phase diagram with three phases (hcp+bcc+liquid) of beryllium has been proposed : - Melting curve is obtained from quantum molecular dynamics (QMD) calculations along isochors. - Using phonon densities of states and a quasi-harmonic model, solid-solid transition is modeled. Our attempt to construct a three phases equation of state (EOS) failed due to our representation of the liquid phase based on Wallace's approach with the bcc phase, instable at low pressure, as reference. Here, we propose to deal with the instability of bcc phase at low pressure and the discontinuity of physical properties at melting. We also present an improved three phases (hcp+cc+liquid) EOS using simple analytic model constrained by the QMD calculations for the liquid. (1) G. Robert and A. Sollier, J. Phys IV 134, 257 - 2006. (2) G. Robert, A. Sollier and Ph. Legrand, to be published in APS-SCCM, June 2007. [Preview Abstract] |
Tuesday, March 11, 2008 3:06PM - 3:18PM |
L40.00004: High Pressure-High Temperature Phase Diagram of Beryllium. W.J. Evans, M.J. Lipp, H. Cynn, B.J. Baer, C.S. Yoo, A. Lazicki, Y. Ohishi, N. Sata A detailed understanding of the phase diagram of beryllium impacts fundamental science and technological applications. Despite a simple atomic structure, theoretical modeling of the phase diagram of beryllium has been extremely challenging and remains an area of active investigation [Kadas, ,PRB 07]. Beryllium is important to a range of applications, including structural members, x-ray windows, and nuclear reactors. Extension of the experimental understanding of beryllium will serve to inform and advance theoretical efforts and technological applications. To address these needs, we have extended our previous work [Evans, PRB 05], and performed x-ray diffraction and melt studies of high temperature beryllium. We will describe our measurements of the crystal structure, lattice constants, and melt curve of high-pressure beryllium. We will discuss insights into this simple yet challenging system. [Preview Abstract] |
Tuesday, March 11, 2008 3:18PM - 3:30PM |
L40.00005: Aluminum Yield Strength on Quasi-isentropes Jeffrey H. Nguyen, J. Reed Patterson, Daniel Orlikowski, L. Peter Martin, Ryan Krone, Roger Minich, Neil C. Holmes Advances in the functionally graded density impactors (FGDI) have made it possible to carry out dynamic experiments at previously inaccessible regions of the phase diagram. We employed these advances in recent tailored dynamic experiments to gain insight into the yield strength of aluminum along ``hot'' quasi-isentropes. The impactor was specifically designed to deliver a triangular compression wave into a sample where the strain rates on the compression and release isentropes were nearly identical. The aluminum samples were initially shocked to a fixed state on the Hugoniot, then quasi-isentropically compressed, and finally allowed to release isentropically. Here, we will discuss the details of the experiments and error analysis in deriving the yield strength of aluminum on a ``hot'' quasi-isentrope. We will also discuss recent advances in the FGDI technology that made these experiments possible with significantly reduced uncertainties. Methods to characterize these advances will be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, March 11, 2008 3:30PM - 3:42PM |
L40.00006: Violation of the London law and Onsager--Feynman quantization in multicomponent superconductors Egor Babaev, Neil W. Ashcroft Non-classical response to rotation is a hallmark of quantum ordered states such as superconductors and superfluids. The rotational responses of all currently known single-component 'super' states of matter (superconductors, superfluids and supersolids) are largely described by two fundamental principles and fall into two categories according to whether the systems are composed of charged or neutral particles: the London law relating the angular velocity to a subsequently established magnetic field and the Onsager--Feynman quantization of superfluid velocity. These laws are theoretically shown to be violated in a two-component superconductor such as the projected liquid metallic states of hydrogen and deuterium at high pressures. The rotational responses of liquid metallic hydrogen or deuterium identify them as a new class of dissipationless states; they also directly point to a particular experimental route for verification of their existence. [Preview Abstract] |
Tuesday, March 11, 2008 3:42PM - 3:54PM |
L40.00007: Ab-initio study on the crystal structure and the superconductivity of calcium in phase IV and V Takahiro Ishikawa, Hitose Nagara, Koichi Kusakabe, Naoshi Suzuki Calcium shows interesting structural phase transitions and the superconductivity under high pressure. Structural transformations from the simple cubic structure (Ca-III) to a complex structure (Ca-IV) at 113GPa and from Ca-IV to another complex one (Ca-V) at 139GPa have been reported, but their structures have not been identified. The pressure-induced superconducting transition has been observed in Ca-III, and the superconducting transition temperature T$_{c}$ dramatically increases at the transition from Ca-III to Ca-IV and reaches to 25K, which is the highest T$_{c}$ in an element, at 161GPa in Ca-V. We explored the structures of Ca-IV and Ca-V via the metadynamics simulation based on the density functional theory and obtained two new structures: A helical structure and a zigzag structure. From comparison of the x-ray diffraction patterns we identified that the helical structure and the zigzag structure are candidate structures of Ca-IV and Ca-V, respectively. For the zigzag structure of Ca-V we calculated T$_{c}$ using the Allen-Dynes formula. We assumed the effective screened Coulomb repulsion constant $\mu $* to be 0.1. We obtained T$_{c}$=18.19K at 140GPa, and the estimated values of T$_{c}$ are high and are close to the experimental values of Ca-V. [Preview Abstract] |
Tuesday, March 11, 2008 3:54PM - 4:06PM |
L40.00008: Pressure-induced insulator-metal and structural transitions of BaBiO$_3$ from first principles LDA+U Davide Ceresoli, Erio Tosatti At zero pressure and temperature BaBiO$_3$ is an insulator with a structural dimerization, equivalent to a static valence disproportionation of the two Bi ions per cell from 4+ to 3+/5+. Under pressure one would expect an insulator-metal transition and the eventual disappearance of the dimerization. Moreover, the metallic phase should be superconducting, in analogy the metal doped Ba$_{1-x}$K$_x$BiO$_3$ compounds. To date, there are no accurate ab initio predictions under pressure, essentially because LDA or GGA fail to stabilize an insulating phase with the correct distortion and electronic gap. We carried out first principles LDA+U calculations by determining the effective Hubbard U self-consistently at every pressure, and found that the presence of U is mandatory for a correct description of the zero-pressure state. Upon increasing pressure, we found an insulator to metal transition at $\sim$~20~GPa. By further increasing the pressure, we predict the appearance of a superconducting phase, characterized by quantum melting of the weakly dimerized CDW lattice. The dimerization tendency and superconductivity are expected to weaken only at much higher pressures, presently under investigation. [Preview Abstract] |
Tuesday, March 11, 2008 4:06PM - 4:18PM |
L40.00009: High pressure magnetic phase transitions in the quasi-2D ferromagnet, CeCrSb$_3$ investigated using designer diamond anvils D.D. Jackson, S.K. McCall, S.T. Weir, A.B. Karki, D.P. Young, W. Qiu, Y.K. Vohra Pressure tuning magnetic phase transitions is a powerful method of discovering new physical properties of materials. At ambient pressure, CeCrSb$_3$ undergoes ferromagnetic ordering at 115~K due to the Cr ions, followed by a gradual ferromagnetic alignment of the Ce moments between 48 and 18~K. The evolution of these magnetic transitions was investigated via electrical resistivity and ac magnetic susceptibility to pressures of 20~GPa using designer diamond anvils. The ferromagnetic ordering due to the Cr ions decreases at a rate of $dT_{Cr}/dP=$-1.75~K/GPa, while the onset of the Ce ferromagnetic ordered phase increases at a rate of $dT_{Ce}/dP = $3.6~K/GPa, followed by a sharp drop at $P_c=$11~GPa. In addition, the electrical resistivity reveals that a possible superconducting phase is found between 11~GPa$ |
Tuesday, March 11, 2008 4:18PM - 4:30PM |
L40.00010: Zirconium Hydride: Structural Integrity at High-Pressures - A Synchrotron X-Ray Difffraction Study Patricia E. Kalita, A. Cornelius, S. Sinogeikin, A. Martin, T. Hartmann, K.E. Lipinska-Kalita Metal hydrides are of great interest not only form the fundamental research point of view but also because of their many technological applications, including hydrogen storage. Here we present our most recent studies in situ, high-pressure, angle-dispersive, synchrotron x-ray diffraction studies of zirconium hydride. We investigate the effects of hydrostatic and non-hydrostatic conditions. We also show the results of structural refinements as well as the bulk modulus of ZrH2. *Work at UNLV is supported by DOE award No. DEFG36-05GO0850. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. Use of the HPCAT facility was supported by DOE-BES, DOE-NNSA (CDAC), NSF, DOD --TACOM, and the W.M. Keck Foundation. Use of the APS was supported by DOE-BES, under Contract No. W-31-109-ENG-38. [Preview Abstract] |
Tuesday, March 11, 2008 4:30PM - 4:42PM |
L40.00011: Structural changes in borohydride hydrogen storage materials Ravhi Kumar, Andrew Cornelius, Malcolm Nicol Angle dispersive powder x-ray diffraction and Raman experiments were performed on ABH$_{4}$ (A = K, Rb) at high pressures up to 27 GPa. We demonstrate that KBH$_{4}$ exhibits structural phase transitions from the ambient $\alpha $-KBH4 phase (cubic Fm-3m) to $\beta $-KBH$_{4}$ (tetragonal-P421c) at 3.8 GPa and to $\gamma $-KBH$_{4}$ phase (orthorhombic-Pnma) at 6.8 GPa which is similar to the phase transition sequence observed for NaBH4 earlier [1]. However, RbBH$_{4}$ undergoes two successive pressure induced structural transitions from the ambient cubic Fm-3m phase to an orthorhombic Pnma phase around 2.9 GPa and then to a monoclinic phase above 8 GPa. The high pressure monoclinic phase is found to be stable up to 27 GPa. The experimental results reveal the phase transition sequence exhibited by RbBH$_{4}$ is different from the pressure induced changes observed in similar cubic compounds NaBH$_{4}$ and KBH$_{4}$. The results further show that both the transition pressure and the structural ordering at high pressures are influenced by the atomic size of the alkali cation in these compounds. [1]. R.S. Kumar and Andrew L. Cornelius, App.Phys.Lett., 2005, 87, 261916. [Preview Abstract] |
Tuesday, March 11, 2008 4:42PM - 4:54PM |
L40.00012: High-stress phases of SiC, GaN, InN, ZnO, and CdSe Kanoknan Sarasamak, Ambarish J. Kulkarni, Min Zhou, Sukit Limpijumnong Phase transformations of SiC, GaN, InN, ZnO, and CdSe from wurtzite (WZ) to three other different crystalline structures under loading of different stress tensors are studied using first-principle calculations. The first transformation studied is well known and occurs under hydrostatic compression and leads to a six-fold coordinated \textit{rocksalt} (RS) structure. The equilibrium pressures for this transformation of the materials are calculated and found to be proportional to the energy difference between the phases at zero stress and vary monotonically with the materials' ionicity. The second and third transformations studied occur under uniaxial stresses and lead to two new crystal structures previously unknown for these materials. Specifically, uniaxial compression along the [0001] direction or uniaxial tension along the $[01\overline 1 0]$ direction, causes a transformation to a five-fold coordinated \textit{unbuckled wurtzite }structure which we named HX. On the other hand, uniaxial tension along the [0001] direction causes the materials to transform into a body-centered-tetragonal structure which we named BCT-4. The critical equilibrium transformation stresses for these transformations are obtained and their correlation with the ionicity of the materials is analyzed. [Preview Abstract] |
Tuesday, March 11, 2008 4:54PM - 5:06PM |
L40.00013: Strength Measurements of Shock-Loaded Ta via Heterodyne Velocimetry J. R. Patterson, J. S. St\"olken, J. H. Nguyen, B. W. Reed, H. Hsieh, M. Kumar While knowledge of the constitutive properties of materials at elevated temperatures and pressures is necessary to understand material behavior under these conditions, experimental measurements are generally sparse. In an effort to explore such material behavior, we have performed several dynamic compression experiments on Ta at the 35 mm-bore single-stage gas-gun facility at LLNL. \emph{In-situ} particle velocities on shock-loading and release were measured by heterodyne( or photonic doppler ) velocimetry. We will present the results of a comparative study among different methods of time-frequency analysis, which is required to extract accurate particle velocities in rapidly varying regions. In addition, we have performed hydrocode simulations employing the MTS model to fit our experimental data. We will discuss these results in the context of extracting the flow stress at pressure. [Preview Abstract] |
Tuesday, March 11, 2008 5:06PM - 5:18PM |
L40.00014: Surface Preparation Methods to Enhance Dynamic Surface Property Measurements of Shocked Metal Surfaces Michael Zellner, Wendy McNeil, George Gray III, David Huerta, Nicholas King, George Neal, Jeremy Payton, Jim Rubin, Gerald Stevens, William Turley, William Buttler This effort investigates surface-preparation methods to enhance dynamic surface-property measurements of shocked metal surfaces. To assess the ability of making reliable and consistent dynamic surface-property measurements, the amount of material ejected from the free-surface upon shock release to vacuum (ejecta) was monitored for shocked Al-1100 and Sn targets. Four surface preparation methods were considered: fly-cut machined finish, diamond-turned machine finish, polished finish, and ball-rolled. The samples were shock loaded by in-contact detonation of HE PBX-9501 on the front-side of the metal coupons. Ejecta production at the back-side or free-side of the metal coupons was monitored using piezoelectric pins, optical shadowgraphy, and x-ray attenuation radiography. [Preview Abstract] |
Tuesday, March 11, 2008 5:18PM - 5:30PM |
L40.00015: Pressure Correction of Density Functional Theory Calculations Shun Hang Lee, Jones Tsz-Kai Wan The modern implementation of density functional theory algorithms involves approximations in the exchange correlation, which leads to discrepancies between experimental measurements and theoretical predictions. In this talk, we present a comparison of exchange correlation approximations by performing first-principles calculations on bulk structures such as MgO, MgSiO3 perovskite and post-perovskite at pressures up to deep Earth conditions. For a given structure, the calculated results such as the equation of state and bulk modulus corresponding to each exchange correlation are compared. At each volume, the pressure estimated by generalized gradient approximation (GGA) is usually above that by local density approximation (LDA,) resulting in a shift in the equations of states. At ambient conditions, such pressure difference is almost independent of pressure and temperature. However, at extreme pressure and temperature such as planetary interiors, this difference becomes temperature and pressure dependent and could lead to large errors in the predictions of properties for minerals at such conditions. In our study, we quantified such a pressure difference at different volume and temperature. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700